1. Field of the Invention
The field of the present invention relates to medical diagnostic tools. More particularly, the field of the present invention relates to systems and methods relating to measuring and reporting a subject""s pain.
2. Background
Pain is an unpleasant sensation, ranging from slight discomfort to intense suffering. But because to a great extent pain is a subjective phenomenon, it has frequently defied objective, quantitative measurement. Traditionally, physicians have had to assess a patient""s pain by relying on the patient""s own description of it. But self-description is not only subjective by definition, it is often inaccurate, in part because it is difficult for subjects to precisely articulate their pain while in the midst of a pain experience.
Moreover, objective assessment of pain is all but impossible in situations where the patient is not fully communicative, such as when the patient is an infant, the patient is not fully conscious or coherent, or the patient is a non-human.
Today, uni-dimensional scales are used to quantify pain. These scales frequently employ verbal (mild, moderate, severe) and numerical (0-10) ratings. Today""s caregivers also use multidimensional scales along with complex, pain diagnosis questionnaires designed to extract as much subjective information as possible from the subject (e.g. sensory, emotional and cognitive).
These pain quantification methods are used in a number of settings. Most commonly, physicians and other health care professionals apply these methods to diagnose and/or treat a patient. Physicians may also use these methods to track the progress of a patient""s illness over time or to determine an amount of pain medication to prescribe to a patient. In other settings, these methods are used to test the efficacy of certain pain-relieving drugs and to establish standard dosages for them. Nonetheless, these methods often lead to inaccurate conclusions because of the subjective nature of the assessment inherent in them.
Logically, pain assessment plays a vital role in determining the amount of pain medication to give a patient. As a result, hospital staff and other health care providers also use visual clues to assess the intensity of a patient""s pain and determine the amount of pain medication to provide. Under this visual assessment method, the caregiver will commonly use a visual analog scale (VAS), usually scored from 1 to 10, to rate a patient""s pain intensity. In a typical scenario, the caregiver will consider different clues to score the patient""s pain intensity, such as facial expressions and cardio-respiratory function, in addition to patient statements of satisfaction.
Notwithstanding the healthcare providers"" diligence, studies have shown that professional caregivers usually give too much or too little pain medication to patients evaluated with these visual scoring methods. Importantly, a caregiver""s failure to give enough pain medication may not only reduce a patient""s quality of life, but may compromise a patient""s ability to fight disease, cause or complicate physiological disorders, and even hasten death. On the other hand, caregivers that overmedicate patients can also cause harmful side effects, including, in extreme cases, patient respiratory arrest.
Some patients also intentionally misrepresent the existence or extent of their pain. These misrepresentations may stem from financial or fiduciary incentives (including a desire for disability payments or insurance damage settlements), chemical dependencies on pain medications, or other patient-perceived secondary benefits to obtaining pain medication. Regardless of the motivation, patient misrepresentation accounts for a significant portion of the demand for pain medication prescriptions. Yet, without any reliable basis for denying such prescriptions, physicians generally must assume that the claims are truthful, even when they may suspect a lack of sincerity. Otherwise, the caregiver may be accused of inhumane treatment. Conversely, other patients may underreport their pain, again for a variety of reasons.
Despite these inaccurate representations, hospitals and other healthcare givers often provide patients with a class of devices known as Patient Controlled Analgesia (PCA) devices. PCA devices employ a type of analgesia system that enables the patient, often in a post-operative setting, to self-administer pain medicine.
Commercial PCA devices include devices such as the Atom PCA Pump 500, APII, Deltec CADD-PCA 5800, Sabratek 6060 and the Verifuse. In a common form of PCA, the patient is provided with a mechanical apparatus comprised of a reservoir and a patient-operable pump. On patient demand, the pump dispenses incremental doses of pain medicine from the resevoir into the patient""s intravenous (IV) system. The device may also comprise a lock-out interval feature that prevents patient remedication for a period of time so as to ensure against over-medication.
While caregivers using VAS methods cannot consistently provide the right amount of pain medication to patients, studies have likewise shown that a patient""s own assessment of satisfaction, even when used in connection with a PCA device, does not reliably indicate when to deliver pain medication. One study shows that although patients may feel satisfied by a regimen of self-administered pain therapy, the majority of those same patients are self-treated below their individual subjective pain thresholds. Forst et. al., Archives of Orthopaedic and Trauma Surgery (Germany), v. 119, p. 267-270, (1999). Moreover, the act of self-medication itself has been found to be unimportant to the issue of patient satisfaction when the patient has sufficient pain relief through medication. Chumbley, et al., Anesthesia (England), v. 54 (4), p. 386-9 (1999).
The present PCA methods and systems also have other drawbacks. For example, they cannot be readily used, if at all, for infants, toddlers, certain spinal cord patients, and others who cannot operate the device or are unable to understand the instructions for controlling the PCA. Also, current PCA devices do not normalize people""s responses, thereby making the subjective nature of pain self-assessment a factor in the operation of the PCA. Even in honest attempts to be objective, patients may rate the same subjective experience of pain differently. For example, one person may rate a certain subjective sensation of pain a xe2x80x9c10xe2x80x9d on the VAS scale whereas another person may rate the same or a similar subjective sensation of pain a xe2x80x9c5xe2x80x9d depending on a variety of psychological factors and life experiences. Thus, without a means to normalize patient self-assessment, PCA devices rely on subjective psychological factors as much as on the type of illness to determine how much pain medicine to provide.
Moreover, self-assessment may lead to inconsistent treatment between different patient types. For example, children who use PCA devices have been reported to frequently experience nausea and vomiting as a result of overdoses, as compared with adults. PCA devices also do not typically reduce the burden on caregivers because, in many cases, the caregivers must repeatedly instruct patients on how to use the PCA devices and monitor their use.
In contrast, previous efforts in pain research have attempted to identify physiological phenomena related to the subjective sensation of pain. Heart-rate, blood pressure, perspiration and skin conductance are some of the physiological phenomena that have been found to be affected by pain. But these physiological phenomena have also been found to be non-specific to pain and, in fact, have been used in other applications, such as polygraphy. Furthermore, these physiological phenomena tend to habituate quickly. Consequently, they are inadequate for objectively assessing pain.
U.S. Pat. No. 6,018,675 issued to Apkarian et al. discloses a pain measurement system based on comparative functional magnetic resonance imaging (MRI) of the brain of a subject. In the disclosed system, measurements quantifying a subject""s pain level are made by comparing images of the subject""s brain when the subject is in pain with the corresponding brain images made when the subject is not in pain. The system therefore generally requires a baseline, pain-free brain image for each subject. Futhermore, the functional MRI-based measurement system is generally a large piece of machinery, is not portable and requires a substantial infrastructure, including trained personnel to operate.
The present invention provides, in one aspect, systems and methods for objectively assessing a subject""s subjective perception of pain.
In a second separate aspect, the present invention is a system comprising a plurality of sensors for measuring electrical activity at a respective plurality of sites on the subject in order to generate a set of electrical activity measurements. The system further comprises a processor for processing the set of electrical activity measurements into a normalized signal, and determining a level value representative of an objective pain measurement for the normalized signal within a predetermined range of frequencies.
In a third separate aspect, the present invention comprises a specific method of objectively measuring a level of pain subjectively perceived by a subject. The method preferably includes the steps of selecting a plurality of sites on the subject for sensing electrical activity, making electrical activity measurements for the plurality of sites, processing the electrical activity measurements into a normalized signal, and determining a level value for the normalized signal within a predetermined range of frequencies.
In a fourth separate aspect, the present invention comprises a computer-readable medium on which are stored sequences of instructions for objectively measuring a subjective perception of pain in a subject. The sequences of instructions are for performing the steps in the method of the third aspect identified above.
In a fifth separate aspect, the present invention is a system comprising means for measuring a subject""s electrical activity at a plurality of sites in order to generate a set of electrical activity measurements. The system further includes processing means for processing the set of electrical activity measurements into a normalized signal, determining a level value for the normalized signal within a predetermined range of frequencies, and scaling the value for the signal into an objective pain measurement.
In a sixth separate aspect, the present invention is a system comprising a plurality of sensors, including a left channel electrode and a right channel electrode. The plurality of sensors measures a subject""s electrical activity at a respective plurality of sites in order to generate at least two sets of electrical activity measurements. The system further comprises a processor for processing the at least two sets of electrical activity measurements into at least two normalized signals, and comparing the at least two normalized signals to each other in order to identify the presence of pain in the subject.
In a seventh separate aspect, the present invention comprises a specific method of objectively measuring a level of pain subjectively perceived by a subject. The method preferably includes the steps of selecting a plurality of sites on the subject for sensing electrical activity, making electrical activity measurements for the plurality of sites, processing the electrical activity measurements into at least two normalized signals, and comparing the at least two normalized signals to each other in order to identify the presence of pain in the subject.
In an eighth separate aspect, the present invention comprises a computer-readable medium on which are stored sequences of instructions for objectively measuring a subjective perception of pain in a subject. The sequences of instructions are for performing the steps in the method of the seventh aspect identified above.
In a ninth separate aspect, the present invention is a system comprising means for measuring a subject""s electrical activity at a respective plurality of sites in order to generate at least two sets of electrical activity measurements. The system further comprises means for processing the at least two sets of electrical activity measurements into at least two normalized signals, and comparing the at least two normalized signals to each other in order to identify the presence of pain in the subject.
In a tenth separate aspect, the present invention comprises a network for objectively measuring pain subjectively perceived by one or more subjects. The network preferably includes at least one signal acquisition subsystem for making electrical activity measurements at a site on each of the one or more subjects, a signal processing subsystem for analyzing the electrical activity measurements and determining analysis values representing different periods of time, and a communication channel linking the signal processing subsystem and the at least one signal acquisition subsystem in order to transmit the subjects"" electrical activity measurements to the signal processing subsystem.
In an eleventh separate aspect, the present invention comprises a pain measurement report comprising a reference to a subject and a value or series of values representing an objective level of pain subjectively experienced by the subject.
In a twelfth separate aspect, the present invention comprises a method of operating a network based on the analysis of pain-related electrical activity measurements. The method preferably comprises the steps of receiving electrical activity measurements on a subject from a testing location, analyzing the electrical activity measurements to obtain an objective pain measurement report, transmitting the objective pain measurement report to the testing location, and receiving non-medical patient information, including, for example, the number of reports, insurance information, incurred costs, patient contact information, patient histories, and patient feedback.
In a thirteenth separate aspect, the present invention comprises an acquisition system for acquiring an objective signal representative of a subjective perception of pain experienced by a subject. The acquisition system preferably comprises a sensor array for measuring an electrical signal at a site on the subject, an amplifier for amplifying the signal, and a band-pass filter for substantially removing components of the signal below about 0.1 Hertz and above about 5 Hertz.
In a fourtheenth separate aspect, the present invention comprises a method of acquiring a signal representative of a subjective perception of pain experienced by a subject. The method preferably includes the steps of detecting an electrical signal at a site on the subject, amplifying the signal, and filtering the signal to substantially remove components of the signal below about 0.1 Hertz and above about 5 Hertz.
In a fifteenth separate aspect, the present invention comprises a system for processing electrical activity measurements taken from a subject. The system comprises a memory for storing the electrical activity measurements and a processor for processing the electrical activity measurements into a normalized signal. A processor is also provided to determine a level value for the normalized signal within a predetermined range of frequencies and to scale the level value for the signal into an objective pain level.
In a sixteenth separate aspect, the present invention comprises a specific method of processing electrical activity measurements taken from a subject. The method comprises the steps of processing the electrical activity measurements into a normalized signal, determining a level value for the normalized signal within a predetermined range of frequencies, and scaling the level value for the signal into an objective pain measurement.
In a seventeenth separate aspect, the present invention comprises a sensor array for measuring electrical activity on the forehead of a subject. The sensor array preferably includes a sensor pad, a left channel electrode positioned proximal to a left edge of the sensor pad, a right channel electrode positioned proximate to a right edge of the sensor pad, a common electrode positioned equidistant from the left channel electrode and the right channel electrode, and filtering circuitry electrically connected to the electrodes in order to filter signals from the electrodes in the range of about 0.1 Hertz to about 5 Hertz.
In an eighteenth separate aspect, the present invention comprises a physiological monitor for measuring multiple physiological signs of a subject. The physiological monitor preferably comprises a system for objectively measuring a subjective perception of pain, in combination with any one or more of a thermometer, a pulse meter, a blood pressure gauge and a respiratory gauge.
In a nineteenth separate aspect, the present invention is a system for delivering medication for reducing pain in a subject. The system preferably comprises a reservoir for containing the medication, a delivery device connected to the reservoir for delivering the medication to the subject, a delivery counter (connected to the reservoir) for measuring the amount of medication transferred between the reservoir and the delivery device, and an objective pain measurement device for objectively measuring a subjective perception of pain experienced by the subject. The system preferably further includes a medication delivery controller in communication with the objective pain measurement device, the delivery counter and the delivery device. The medication delivery controller preferably controls the amount of medication delivered to the subject by the delivery device based on a delivery rate communicated by the delivery counter and an objective pain measurement communicated by the objective pain measurement device.
In a twentieth separate aspect, the present invention is an electrical signal containing information objectively describing an intensity of a subjective experience of pain in a subject. The electrical signal is obtained by a process comprising the steps of selecting a site on the subject for sensing electrical activity, detecting electrical activity from the site, and filtering the electrical activity within a frequency range of about 0.1 Hertz to about 5 Hertz.
The foregoing methods may be implemented in the form of systems, devices, and computer-readable media. Further embodiments as well as modifications, variations and enhancements of the invention are also described herein.